A flora (with a lower case 'f') refers to the plant life occurring in a particular region, generally the naturally occurring or indigenous plant life. Botanists and paleobotanists use the term to refer to a typical collection of plants found in a specific time or place, e.g. the "Sonoran Desert flora" or the "Caenozoic flora". It also can refer to a given subset of the flora of a given region, as in: "... Southern Africa has a rich Ericaceous flora ...".

A Flora (with a capital 'F') refers to a book or other work describing a flora and including aids for the identification of the plants it contains such as botanical keys and line drawings that illustrate the characters that distinguish the different plants. Floristics is the study of floras, including the preparation of Floras.

Plants are grouped into floras based on region, period, special environment, or climate. Regions can be geographically distinct habitats like mountain vs. flatland. Floras can mean plant life of an historic era as in fossil flora. Lastly, floras may be subdivided by special environments:

Native flora. The native and indigenous flora of an area.

Agricultural and garden flora. The plants that are deliberately grown by humans.

Weed flora. Traditionally this classification was applied to plants regarded as undesirable, and studied in efforts to control or eradicate them. Today the designation is less often used as a classification of plant life, since it includes three different types of plants: weedy species, invasive species (that may or may not be weedy), and native and introduced non-weedy species that are agriculturally undesirable. Many native plants previously considered weeds have been shown to be beneficial or even necessary to various ecosystems.

Bacterial organisms are sometimes included in a flora,[1][2] and sometimes the terms bacterial flora and plant flora are used separately.

Traditionally floras are books, but some are now published on CD-ROM or websites. The area that a flora covers can be either geographically or politically defined. Floras usually require some specialist botanical knowledge to use with any effectiveness.
It is said that the Flora Sinensis by the Polish JesuitMichał Boym was the first book that used the name "Flora" in this meaning, a book covering the plant world of a region.[3] However, despite its title it covered not only plants, but also some animals of the region.
A flora often contains diagnostic keys. Often these are dichotomous keys, which require the user to repeatedly examine a plant, and decide which one of two alternatives given in the flora best applies to the plant.
A compendium of world floras has been compiled by David Frodin.[4]